The present invention relates to an intermittent driving mechanism such as a carriage driving mechanism in a printer. More specifically, the invention relates to a vibration preventing device for preventing vibration from being produced at the time of stopping a driven member having a specified mass such as a carriage.
FIG. 1 of the accompanying drawings is a plan view of a pen printer. In this printer, recording paper (not shown) is fed out in the direction (X direction) orthogonal to the sheet of FIG. 1 by a rotatable platen 2 mounted on a base 1, and a carriage 3 is moved laterally (Y direction) as shown in FIG. 1. Then, one of plural pens P mounted on the carriage 3 is pressed by a hammer 4 to bring the tip of the pen into contact with the recording paper. Simultaneously, the pen is controlled to move in the above X and Y directions so as to record desired characters, signs or figures.
In the above printer, the power of a stepping motor Mx is transmitted through a gearing 5 to the platen 2 to rotate the platen 2. The power of a stepping motor My is also transmitted from a pinion 6 secured to a rotatable shaft m through an intermittent gear 7 to a gear 8, for thereby driving a drum 8a integral with the gear 8. By a wire 9 wrapped round the drum 8a, the carriage 3 can be driven along a guide shaft 3a. The foregoing components for transmitting the driving force to the carriage 3 constitute an intermittent driving mechanism 10.
In the intermittent driving mechanism 10 described above, the carriage 3 (a driven member having a specified mass) with the pens P mounted thereon is intermittently moved by the stepping motor My. When such movement is stopped, a driving system such as a rotor of the motor is subjected to damping vibrations due to inertia of the carriage 3 or characteristics of the stepping motor. Such damping vibrations make the recording operation of the printer unstable.
In order to cancel such vibrations, there has conventionally been provided a vibration preventing device as shown in FIG. 2. In the conventional vibration preventing device, a resistance plate 11 is pressed against a rotatable shaft m of a stepping motor My to apply a fixed frictional resistance to the rotative power of the stepping motor My, with the result that the generation of vibrations in a driving system can be prevented when the stepping motor My stops.
With the above prior vibration preventing device, however, as the fixed resistance is always applied to the rotatable shaft m by the resistance plate 11, a large load is imposed on the stepping motor My. Especially at the time of starting the stepping motor My, large power is required by the motor. This results in the disadvantage is that excessive power consumed.